Carbon allotropes are some of the best studied materials for more than 3000 years. The commonly known natural types are the coal, graphite and diamonds. The other synthetic carbons are amorphous carbon, buckminsterfullerene and carbon nanotubes.
Natural sources of carbon are considered as usable, but natural sources are not available universally on the earth. Natural sources can also lead to an environmental crisis.
Hence there are various methods developed by researchers using different carbon “C” containing precursor materials to synthesize carbon. The starting “C” containing precursor may be natural or synthetic materials that contain elemental carbon “C” in its composition.
The most known method to produce carbon is from petroleum byproducts. But there are other common known processes where the natural biomass is converted into carbon material which is environmentally friendly.
The carbonization, preparation process temperature, physical condition and the starting precursor define the amorphous, porous and crystalline characteristic of the carbon.
Amorphous carbon with porous structure (activated carbon) is a well-known material for industrial applications and is in huge demand. The surface area of the activated carbon can reach up to 3000 m2/g.
Most of the activated carbon is produced from charcoal, pet coke, diesel oil, used tires, coconut shell, wood, and agricultural wastes. In practice, coal and coconut shell are the two main sources for the production of activated carbon.
There are two ways for the activation process, namely, physical and chemical activation. The physical activation is done under CO2, dry air and steam (H2O) activating agents, where the activating agent physically adsorbs on the surface of the carbon. In the chemical activation process, the carbon precursor is impregnated with chemical activating agents such as LiOH, H3BO3, NaOH, Na2CO3, Na2S2O3, Na2S, KOH, KCl, K2CO3, CaCl2, P2O5CsOH, AlCl3, MgCl2, ZnCl2, FeCl3, FeSO4, RbOH, HCl, H3PO4, H2SO4, HNO3, H2O2, etc.; and heated (pyrolysis) in an inert atmosphere (Ar, N2) at different temperature range 400-1200° C. The activation and the heat treatment (pyrolysis) under various gases can be done in a single step or in multiple steps. The surface area observed in these processes is in the range of 300-3000 m2/g.